TUESDAY, Nov. 3, 2015 (HealthDay News) -- The more children a woman has, the lower her risk of ovarian cancer may be, a new study suggests.

The study also found that the risk is lower in women whose fallopian tubes have been tied -- a procedure called tubal ligation.

British researchers analyzed data from more than 8,000 women to determine risk factors for the four most common types of ovarian cancer: serous, mucinous, endometrioid and clear cell tumors.

"In the last few years, our understanding of ovarian cancer has been revolutionized by research showing that many cases may not in fact come from the ovaries. For example, many high-grade serous tumors -- the most common type -- seem to start in the fallopian tubes, while some endometrioid and clear cell tumours may develop from endometriosis," lead researcher Kezia Gaitskell said in a Cancer Research U.K. news release.

Compared to women with no children, those with one child had a 20 percent lower overall risk of ovarian cancer and a 40 percent lower risk of endometrioid and clear cell tumors. Each additional child offered an additional 8 percent reduction in overall ovarian cancer risk, said Gaitskell, who is a pathologist in the University of Oxford's Cancer Epidemiology Unit.

Further investigation showed that women whose fallopian tubes had been tied had a 20 percent lower overall risk of ovarian cancer; a 20 percent lower risk for high-grade serous tumors; and a 50 percent lower risk for endometrioid and clear cell tumors.

The study was to be presented Tuesday at a meeting of the U.K.'s National Cancer Research Institute, in Liverpool. Research presented at meetings is typically considered preliminary because it is not subject to the same scrutiny as studies published in medical journals.

It should be noted that the study uncovered a link, but not a cause-and-effect connection, between the number of children a woman has and her risk of ovarian cancer.

The increased risk among women with no children is believed to be related to infertility. Gaitskell noted that some conditions -- such as endometriosis -- that make it harder for a woman to get pregnant may also increase her risk for specific types of ovarian cancer.

As for the reduced risk among women whose tubes had been tied, Gaitskell said tubal ligation may help prevent abnormal, tumor-causing cells from reaching the ovaries.

"Our results are really interesting, because they show that the associations with known risk factors for ovarian cancer, such as childbirth and fertility, vary between the different tumor types," she concluded.

Conference Chairman Charlie Swanton, a professor of cancer medicine at the University College London Cancer Institute, said in the news release that the new research expands on existing knowledge.

"We've known for some time that the number of children a woman has, and her use of contraception, can influence her risk of ovarian cancer, so this research provides important further detail about different types of the disease," he said.

Swanton noted that ovarian cancer, like many other cancers, is not one disease, but different diseases that are grouped together because of where they start.

"It's important to know what affects the risk of different types of ovarian cancer, and what factors impact this. We now need to understand the mechanisms behind these findings to develop some way to extend this lower risk to all women, regardless of how many children they have," he concluded.